1. Field of the Invention
This invention relates generally to waterbeds, and more particularly to systems for reducing undesirable wave motion within waterbed mattresses in response to movement of individuals sitting or lying on such mattresses.
This invention also relates generally to fiber products and to methods for their manufacture, and more particularly to a bonded fiber product previously shown to be useful when placed directly within a waterbed mattress--and here shown to be useful when placed within a float that is used to support a wave-retarding baffle in a waterbed mattress.
2. Prior Art
(a) Hanging baffles in general--Some systems for reducing wave motion within waterbed mattresses use a baffle or baffles hung from a buoyant structure or structures. In some cases the baffle is contoured in various ways, and in particular when the baffle is contoured to form a closed or nearly closed structure it has been called a "hydraulic chamber".
In all hanging-baffle systems, wave energy is expended (against internal friction of the water) in moving the baffle--and also, more importantly, in moving a body of water that is behind or within the baffle.
(b) Hydraulic chambers--A hydraulic chamber is a preferably nonwatertight inner compartment which damps undesirable waves by the inertia and internal friction of enclosed water. Because it is vented, a hydraulic chamber allows relatively slow inward and outward water flow, to accommodate filling of the mattress--and to accommodate relatively slow shifts of water distribution, thereby helping the waterbed mattress to adjust to the position of a person lying on the bed.
The unsealed apertures in the chamber are small enough, however, to cause the chamber to behave essentially as a unit in response to transients caused by relatively abrupt motions of the occupant. This latter effect helps to resist and thereby reduce the undesirable wave motion.
(c) Floats in general--Hydraulic chambers have been supported by buoyant structures or "floats" of various kinds, including buoyant pads, sheets or blocks of polyethylene foam, within the mattress. Typically the buoyant structure floats just below the upper panel of the mattress, and the chamber hangs toward (but generally not all the way to) the bottom panel of the mattress.
Such buoyant structures, with hanging baffles attached, help to inhibit formation as well as propagation of waves within the mattress. They also impart a relatively firm "feel", since they float immediately below and in contact with the mattress top panel, and so can be felt by a user/occupant. Many users prefer such a firm "feel"; however, generally they do not like to distinctly sense the buoyant structure itself or the baffle itself as a distinct object. Consequently a layer of fiber is generally or often added on the top of the buoyant structure.
(d) Polyethylene-foam pads as floats--Prior buoyant pads used to support hydraulic chambers have been made of polyethylene. Unfortunately, even closed-cell polyethylene has a tendency to slowly waterlog and eventually sink. A representative of the Dow Chemical Company, which makes this material, has explained to me:
"Under long-term submersion conditions, polyethylene foam sheet can be expected to pick up some quantity of water, even though the foam has a closed-cell structure. This is due to the slow migration of individual water molecules into and through the polyethylene cell walls. The buoyant force exerted by the foam would, of course, decrease as more and more water molecules make their way into the foam."
This manufacturer estimated the length of time required for this effect to become significant, under conditions pertinent to waterbeds, as "certainly a number of months and possibly several years," and went on to say "we have no data that would allow us to refine this further." I have heard reports of hydraulic-chamber floats waterlogging and sinking in as short a time as eight months, and even six.
Besides forfeiting its antiwave characteristics, a chamber or other continuous structure which sinks can also obstruct convection at the waterbed heater and thermostat. Depending on the geometry and on the electrical circuitry of these devices, various adverse conditions may result--such as causing the thermostat and heater to cycle on and off frequently, and/or to wear out entirely; and/or causing the heater to stay off continuously or to stay on continuously. In the last-mentioned case, accumulated heat could damage the mattress and liner, possibly even releasing the water from the mattress and causing water damage to the premises in which the mattress is installed.
Some mitigation of the uptake of water by polyethylene foam may be obtained by using relatively high-density foam. High-density foam presents a greater number of cell walls through which water must migrate to occupy the foam. Unfortunately, however, any material with higher density has correspondingly lower buoyancy, and polyethylene foam is no exception. Thus the manufacturer using floats made of polyethylene foam has a choice of providing brief buoyancy or lower buoyancy! The cost, weight and bulk implications of the latter are apparent. Bulk, in particular, is undesirable since it places a lower limit on the overall size of the unfilled waterbed mattress for shipment and storage.
One seductive solution to this problem is to encapsulate the polyethylene foam pad in vinyl--or in some other sheeting similar to that used for the mattress proper. There are several drawbacks to this solution, the most pertinent ones for present purposes being that the polyethylene foam remains relatively bulky for shipment.
(e) Inflated floats--In a related system, a hydraulic chamber is supported from a float that is buoyant by virtue of being inflated. In other words, this system uses a float which encapsulates air (or other gas).
The difficulty with this system is that consistent buoyancy is obtained with such a float only if the inflation pressure is adequate to maintain the shape and thus the volume of the float roughly constant. Unfortunately, however, if inflation pressure is high enough to satisfy this condition, the float is relatively stiff and rigid. Whenever there are minor movements of the water within the mattress, therefore, the float bumps very noticeably against the underside of the upper panel of the mattress--and thus against the occupant of the bed.
In summary, the inflated float suffers from either inconsistent buoyancy or excessive rigidity.
(f) Nonbuoyant fibrous matting used as a wave absorber--Other systems make use of fibrous mats placed within waterbed mattresses to absorb the energy of water motion caused by occupant movement; this is the subject of my U.S. Pat. No. 4,301,560. In these latter systems energy is absorbed in the flow of water through the bonded nonwoven polyester fibrous structure of the matting.
This approach to reducing wave motion can be used to provide a relatively soft "feel," preferred by some users. This kind of "feel" generally results from using fiber that is not significantly buoyant. (My U.S. Pat. No. 4,301,560 is not limited to providing this softer "feel.")
(g) Summary of the prior art--All of these various configurations strongly affect the "feel" of the finished mattress. As already noted, different users typically prefer different configurations.
In any wave-retarding article placed within a waterbed it is desirable that the design provide for some degree of optimization of the mechanical characteristics of the article at the time of manufacture, so that it can be inoffensive in its contact with the occupant of the bed.
A soft "feel" is readily attained by my waterbed mattress with fibrous-matting wave retarder. A harder "feel" is provided by hanging baffles (and particularly hydraulic chambers), but the technology of providing suitable floats is not yet satisfactory from all viewpoints.
In particular, polyethylene floats tend to sink unless encapsulated, and if encapsulated they are bulky in shipment. Inflated floats require excessive inflation pressures or bump against the occupant of the bed, and thus are not amenable to optimization of mechanical characteristics as noted above.
Earlier teachings thus fall short of providing a buoyant article for support of a hydraulic chamber that can be installed, shipped, and used economically.